1. Technical Field
The present invention relates to a power transmission apparatus for a compressor used for an air conditioning system for a vehicle, and more particularly, to a power transmission apparatus for a compressor, which cuts off power transmission from an engine to the compressor when overload occurs in the compressor.
2. Discussion of Prior Art
With reference to FIG. 1, a conventional power transmission apparatus for a compressor will be described. A pulley 145 is rotated by a driving power transmitted from an engine, and a hub 140 is connected to a driving shaft of the compressor. A limiter 110 is installed between the pulley 145 and the hub 140, so as to transmit power. When a torque being or above a predetermined value occurs in the compressor, the limiter 110 cuts off the power transmission between the pulley 145 and the hub 140. A damper 120 is integrally formed around an outer circumference of the limiter 110, to absorb an impact. Semicircle-shaped protrusions are formed on an outer circumferential surface of the damper 120 at predetermined intervals.
A fixed cover 130 is connected to an outer edge surface of the damper 120. The fixed cover 130 prevents separation of the damper 120 and is fixed to the hub 140. A dust cover 135 facing one side of the hub 140 is connected to the pulley 145, together with the fixed cover 130. The dust cover 135 prevents broken pieces of the limiter 110 from scattering to the outside.
In the aforementioned conventional power transmission apparatus for a compressor, a driving power transmitted from the engine is transmitted to the compressor to be driven. The driving power transmitted from the engine to the pulley 145 is transmitted to the fixed cover 130 connected to the pulley 145 and is transmitted to the limiter 110 through the damper 120 inside the fixed cover 130. Then, since the limiter 110 is connected to the hub 140, the hub 140 is rotated by rotation of the pulley 145 and the driving shaft of the compressor connected to the hub 140 is rotated so that the compressor is operated. Therefore, the air conditioning of a vehicle is performed, using circulation of refrigerant which is compressed and discharged according to the driving of the compressor.
When the compressor stops rotating due to a defect thereof, the hub 140 connected to the driving shaft of the compressor stops rotating. However, since the pulley 145 connected to the engine is rotated by the driving power provided by the engine, the driving power acts on the fixed cover 130 connected to the pulley 145 and the damper 120 positioned inside the fixed cover 130. Accordingly, since an outer ring 112 part of the limiter 110 formed integrally with the damper 120 attempts rotation while an inner ring 111 part of the limiter 110 connected to the hub 140 resists rotation, a torsion torque is generated in a bridge 113 connecting the inner ring 111 and the outer ring 112. When the torsion torque increases and the bridge 113 is not able to endure the torsion torque, the bridge 113 breaks. Accordingly, the pulley 145 is capable of rotating even though the hub 140 is not rotated. A belt connecting the engine and the pulley 145 is not damaged.
When the power is transmitted or cut off, the damper 120 attached to the outer circumferential surface of the limiter 110 repeats constriction and stretch to absorb an impact upon the power transmission or cut-off.
When the limiter 110 is broken by the torsion torque, broken pieces of the bridge 113 connecting the inner ring 111 and the outer ring 112 may scatter. However, since the dust cover 135 covering the limiter 110 and the damper 120 is connected to the one side of the pulley 145, the broken pieces of the bridge 113 are prevented from scattering to the outside. That is, the dust cover 135 prevents the broken pieces of the bridge 113 from affecting the engine and others and prevents error operation of the limiter 110 by protecting the limiter part from external foreign materials.
Further, since the dust cover 135 is installed, water is prevented from directly flowing into the connection part between the limiter 110 and the hub 140 or into the pulley 145, thereby delaying corrosion of main parts of the power transmission apparatus and improving durability of the parts, such as bearings.
However, in the conventional power transmission apparatus for a compressor, since the limiter 110 and the damper 120 are formed integrally with each other, it is not easy to manufacture the limiter 110 and the damper 120. Moreover, since the damper 120 and the fixed cover 130 are formed in a complicate shape, it is not easy to perform a press process of the fixed cover 130.
Specifically, since the limiter 110 and the damper 120 are manufactured integrally, the materials thereof cannot be different. Accordingly, in manufacturing the integrally formed limiter 110 and damper 120, materials to satisfy the performance of limiter 110 or damper 120 has to be used. In the conventional art, the damper 120 is manufactured using the materials having fragility to satisfy the performance of the limiter 110. As a result, since both of the limiter 110 and the damper 120 are made of the materials having fragility, there is a problem in that the damper 120 is easily broken.
The aforementioned problem is found in U.S. Pat. No. 7,066,819 which is a conventional art in this technological field. That is, in a hub connecting a shaft and a pulley, an inner cylinder connected to the shaft is formed inside a disk, an outer circumferential member connected to the pulley is positioned outside the disk, and a damper is integrally formed between an edge of the disk and the pulley. The inner cylinder includes a relatively thin part which is broken upon over load. Therefore, since the disk, the damper and the part being broken upon over load are integrally formed in the hub, U.S. Pat. No. 7,066,819 has the aforementioned problems.